If you are in charge of managing content for any AutoCAD using business that works in multiple units like metric and imperial, then you may be in for quite an unpleasant surprise when you attempt to implement Annotative Scaling.

In the illustration to the right I show a simple callout Block being inserted into a drawing.  Typically Blocks will read the Insertion Scale value, found on the Drawing Units dialog, and react accordingly.  Drawings created in Inches will convert to Millimeters when Inserted into a drawing where the "InsUnits" value has been set to "4" (Millimeters).  Advanced users can, of course, tinker around with "InsDefUnitsSource" and "InsDefUnitsTarget" to create other results but generally most would expect a simple and automatic conversion.

If you set your Blocks to use Annotative Scaling, they will ignore the "InsUnits" value!

I work in Imperial units so I never really gave scaling much thought until I had to update content libraries for some of my clients who work in both Imperial and Metric units.  Not only do they work in Imperial and Metric units but in variations of both; i.e., inches, feet, millimeters, centimeters and meters.

I'm mad at Autodesk for not revealing that Blocks set to use Annotative Scaling don't read the "InsUnits" because this is a major flaw that deviates from an expected pattern.  Fortunately I did not convert everything and I kept a backup copy, but I did convert all of the Callouts, taught groups how they worked and assumed all was okay.  I soon discovered that all was not okay and I just couldn't believe that "InUnits" was being ignored until I found this comment in the Help document: "Note: The INSUNITS setting is ignored when inserting annotative blocks into a drawing".

The reason the sample Tool Palette offers copies of each tool for Imperial and Metric is due to this stupid limitation.

Annotation Scaling is relative to the original scale of the Object so rather than duplicate all of the work by making metric Blocks, I created scaled versions of the original Imperial set.  Ironically this is exactly what the "InsUnits" variable is designed to do so I am at a complete loss as to why Autodesk disabled it for Annotative Scaled Blocks.

In the illustration to the right I show an example Tool Palette for millimeter use where an Imperial set of tools has been set to insert Annotative Scaled Blocks by a scale of "25.4"

The solution I describe above works pretty well for a two unit system, Inches and Millimeters, for example, but if you have to offer the same set of Blocks for Inches, Feet, Millimeters, Centimeters and Meters it requires a copies of the Tools for each unit of measurement.